One of the crucial steps of planning and optimizing a trajectory for any air vehicle (e.g., commercial or military aircraft, missile, helicopter or unmanned air-vehicle) is the construction of a sequence of actions that addresses all the constraints of the flight coming from the specific air vehicle mission in an optimum and flyable way.
In Air Traffic Management (ATM), there may be many different constraints to the trajectory that an aircraft must follow, constraints that may relate to given waypoints along which the aircraft must pass during the flight, or to certain speeds or altitudes to which the aircraft must restrict when passing along certain areas.
Therefore, the aforementioned sequence of actions may establish what maneuvers (along with the specific order within they should come into effect) the aircraft should perform in order to meet the requirements set out by the given constraints.
As has already been said, constraints usually refer to requirements such as geographical positions, speeds or altitudes that the aircraft must comply with during the flight. Constraints do not normally precisely define what low level actions (i.e. flaps position, landing gear position, speed brake position, etc.) the aircraft must perform in order to meet the requirements; the latter is left to the arbitrariness of the pilot or Flight Management System (FMS), as long as the final trajectory followed by the aircraft satisfies the given constraints.
Thus, in order to meet the constraints, sequences of actions to be performed by the aircraft are defined according to a specific schedule. This specific schedule according to which actions to meet the flight constraints are defined and listed in a sequence of actions are called “micro-strategies”.
In a first instance, a horizontal profile (also called lateral profile) for the flight is defined. This profile establishes the horizontal path to be followed by the aircraft so that it passes along the coordinates or waypoints that the operator (e.g., airline) has established for the specific flight. Accordingly, the horizontal profile establishes the actions (for the case of a Horizontal Profile defined geographically, these actions may refer either to turning maneuvers (geodesic or circular arcs), constant bank angle turns, constant heading segments, etc.) to be performed by the aircraft in the different flight segments (FS) in which the entire flight is divided. Each flight segment (FS) is defined (again for the case of a Horizontal Profile defined geographically) by two along-track distances.
In general, a Flight Segment is defined by two triggers, which represent respectively an initial and a final state of the aircraft, between which an action should be performed by said aircraft in order to conform to a certain flight constraint imposed for that Flight Segment.
For example, a constraint may indicate that the aircraft should decrease its altitude in 10,000 feet when flying from waypoint A to waypoint B (trigger A and trigger B, defining a Flight Segment of a geographical Horizontal Profile). Thus, the aircraft should perform an action for fulfilling the condition imposed by that constraint.
In a second instance, a vertical profile (also called longitudinal profile) for the flight is defined. This profile establishes the ascent and descent maneuvers, along with the acceleration and deceleration maneuvers to be performed by the aircraft, in order to meet the altitude and speed constraints.
The output of the vertical profile definition process is a sequence of ascent-descent maneuvers, acceleration-deceleration maneuvers or their combination (alternated with steady-state periods) to be accomplished by the aircraft, each maneuver being specified by an initial and final trigger within which the maneuver should take place.
Finally, in a third instance, a configuration profile for the flight is defined. This profile establishes a sequence of “low level” actions (actions defined in more detail) to be executed by the aircraft so that the aircraft flight complies with the restrictions imposed by the given constraints; these “low level” actions refer to the extensions and retractions of either the landing gear, speed brakes or high lift devices, so that the aircraft can accomplish the actions previously defined in the Horizontal and Vertical Profile without violating certain performance limitations (typically, minimum or maximum speeds).
The output of the configuration profile generation process is a sequence of extension-retraction maneuvers (alternated with steady-state periods) to be executed by the aircraft, each maneuver being specified by an initial and final trigger within which the maneuver should take place.
The configuration profile is defined in accordance with the maneuvers which are previously defined in both the horizontal profile and the vertical profile.
The construction of the abovementioned sequences of actions is a complex task, since there are different kinds of constraints that cannot be addressed independently, as they are interrelated and the process should ensure compliance with the air vehicle performance characteristics.